1. Field of the Invention
The present invention relates to a solid state image pickup apparatus, a camera and a driving method of a solid state image pickup apparatus, and more particularly to an apparatus and a method which is suitably applied to a CMOS area sensor.
2. Description of Related Art
A charge coupled device (CCD) has been conventionally known as a solid state image pickup device, which converts an image signal into an electric signal. The CCD has a photodiode array, and is configured to apply a pulse voltage to charges stored in each photodiode to read the stored charges as an electric signal.
Moreover, in recent years, a CMOS area sensor, in which photodiodes and MOS transistors are produced on one chip, has been used as a solid state image pickup device. The CMOS area sensor has the following advantages: power consumption is small; drive power is small; speeding up becomes possible; and the like, in comparison with a CCD. Consequently, it is expected that the demand of the CMOS area sensor will be expanded in the future.
And a proposal of expanding the dynamic range of a solid state image pickup device using such a CMOS area sensor has been provided (Japanese Patent Application Laid-Open No. 2001-186414 (see corresponding U.S. Pat. No. 6,307,195)).
In the CMOS area sensor in such a proposal, each pixel includes a photodiode, a floating diffusion (hereinafter referred to an FD as the need arises) region, a transfer transistor for transferring charges from the photodiode to the FD region, and a reset transistor for resetting the FD region to predetermined potential. The CMOS area sensor is composed of such pixels arranged in a matrix.
The CMOS area sensor is configured as follows. That is, first, a signal based on charges stored in the photodiode is read, and after that, a signal based on the charges which have overflown the photodiode and have been stored in the FD region is read. Then, the read signals are output through an analog amplifier.
However the prior art needs signal reading two times, and outputs those signals through the analog amplifier. Consequently, an excessive restriction arises in the operation speed of the CMOS area sensor. Consequently, the prior art has a problem of the difficulty of suitably picking up a moving image which needs a high speed reading in real time when the prior art is used.
The present invention has been made in view of such a problem. It is an object of the present invention to provide a solid state image pickup apparatus capable of reading a signal at a high speed while securing a wide dynamic range, its driving method, and a camera using the solid state image pickup apparatus.